For many years, systems have been designed to carry fluids, both liquid and gas. In many of these systems, valves are critical considerations. They can be used to direct fluids to specific destinations, or to allow for isolation of components within a fluid carrying system for maintenance or replacement. In other systems, certain valves serve as safety features. In any system, from the most basic to the most intricate, the means for actuating the valve is a critical variable which must be appropriate to the specific application.
Several alternative means exist for effecting valve operations. One option is to manually manipulate the valve. For example, U.S. Pat. No. 5,265,840 discloses a manually operated pinch valve, where pressure is applied directly to a trigger, which is fixed to an actuator and pinching means, all of which are aligned in a substantially co-axial manner. Depressing the trigger therefore causes the actuator to operate against the force of a spring, thereby moving a dome block (pinching means) away from a resilient tube, allowing the tube to open. This type of application is suited for applications where an individual is holding an instrument which contains pinch valves.
Certain applications make it infeasible or impractical to manipulate the valve by human force as described above. Independent and/or remote operation is desired in many applications where the valve acts as a safety related isolating or activating means. For example, a standard safety feature for a system carrying a hazardous or dangerous composition, is to provide an actuator which isolates a leak in the system either automatically upon detection of the leak or by remote, manual means. Another example of a system in which a remotely or automatically actuated valve which is desired is a sprinkler system used to combat fires. An example of this type of remotely operated valve is disclosed in U.S. Pat. No. 5,343,884. This patent discloses a self closing gate valve which uses a compressed spring acting against a valve actuating arm to force the valve shut. The spring is held in a compressed position by clips and a sleeve. The spring is released either when the clips melt, as caused by a fire, or by manually retracting the sleeve from a remote location by use of a cable. Thus, should a fire break out, either the clips will melt, thereby allowing the spring to operate against the actuating arm, or if an individual discovers the fire prior to the melting of the clips, the individual discovering the fire can manually manipulate the cable, thereby moving the sleeve holding the spring to achieve the same valve operation. The valve in this type of system is designed for only a single operation, i.e., sprinkling due to a single fire. After the single operation, the system must be reset and parts (clips) replaced. Thus, while effective for a particular use, this type of system has very limited use in other applications, and even may be undesirable for its intended use since it is conceivable that a fire could follow another before an individual has an opportunity to repair or replace the valve.
In other applications, remote operation is primarily a function of the desire to automate a process for practicality, expediency, or efficiency. This type of system may use a motor operating either a cam or a gear to directly force the stem of a valve to the desired position. These systems are particularly useful in cases where it is desired to re-position the valve more than once, or in a particular sequence. For example, U.S. Pat. No. 5,584,320 discloses a motor driven device for control of fluid flow through a plurality of tubes. In this device, a plunger is held against a tube by a spring to stop the flow of fluid through a tube. To open the tube, a motor shaft turns a roller cage which results in rollers being forced against the plunger, thereby forcing the plunger away from the tube and allowing fluid to flow through the tube. By providing a plurality of concentric rollers, a single tube can be opened or shut in a predetermined pattern. Locating the rollers coaxially allows a series of tubes to be controlled.
Alternatives to the motor and cam system are available in solenoid and piston operated valves. Solenoid operated valves replace the motor and cam with a coil, a metal core, and activating current. The metal core either operates against the stem of the valve, or is the stem of the valve. Typically, a spring holds the stem in a first position. The magnetic field, when activated, forces the stem into a second position. Depending on the particular application, the valve may be normally open or normally shut when it is de-energized. U.S. Pat. No. 4,259,985, for example, discloses the use of a solenoid to operate a three-way pinch valve. Three-way pinch valves are well suited as a zero dead volume switch valves, meaning that a sample may be withdrawn from one location and directed to a second location with minimal waste of fluid. Systems utilizing a piston rely on a fluid, either liquid or gas, operating against a piston to reposition the valve. A fluid system is disclosed in U.S. Pat. No. 3,882,899 in conjunction with a three-way pinch valve designed to shut the initially open tube before allowing the initially shut tube to open.
Of course, for any given application, more than one type of actuator may be appropriate, and the actual choice will be driven by other considerations such as, but not limited to, cost, dependability, and availability of power. While all of these are effective in a wide variety of applications, recent developments within the fields of medical and pharmaceutical research highlight the shortcomings of the above systems.
The fields of medical and pharmaceutical research are laboratory intensive endeavors necessitating significant repetition of and alteration to specific experiments. One example of this is pharmacokinetics research. In this type of testing, it is not unusual to inject predetermined amounts of chemicals into a test animal at periodic intervals. The animal's body fluids, such as blood or bile, can then be sampled for the drug and drug metabolites to calculate the tissue concentrations. In experiments of this nature, it is desired to place the valves which control the sampling process as close to the animal as possible in order to minimize the amount of fluid which must be extracted in collecting the proper sample. Additionally, the valve must be as unobtrusive as possible, so that the animal's activities are not unduly altered, since the physical activity may be a significant element of the test. Pinch valves are particularly useful in these applications. Pinch valves can control fluid flow through resilient tubes without the need for contacting the fluid being controlled. Thus, the valve can be reused without fear of cross-contamination. Further, there is no need for special coatings on the valve, such as anticoagulation coating when the fluid is blood. As in any application, expenses, failures, and maintenance efforts must be kept to a minimum. As is explained below, each of the valve systems outlined above, even those which incorporate pinch valves, have shortcomings if used for this type of research.
The device of U.S. Pat. No. 5,265,840 must be manually activated. Consequently, an individual must be in close proximity to the animal resulting in changes to the test animal's behavior. Alternatively, the valves could be located away from the animal, requiring an extreme amount of fluid to be withdrawn in order to collect a sample. Further, the need for a coaxial relationship between the trigger, actuator, and pinching means significantly limits the potential for using this device in testing situations. Finally, such manual actuation requires that the individual be able to recognize and react (activate the valve) to changes in animal behavior instantaneously in order to properly control the fluids in the system.
Motor operated valves such as that disclosed in U.S. Pat. No. 5,584,320, also suffer from several deficiencies. It is difficult to miniaturize a valve, motor and cam so that they can be located near the animal. Even if such miniaturization were accomplished, a power line to the motor would be required. Such a power line is cumbersome and consumes precious space near the valve. Additionally, the motor and cam can be noisy, thereby distracting the animal. Further, the added complexity of the motor and cam increases costs both for initial acquisition and also for maintenance.
Piston operated valves suffer from the additional problem of requiring a complex support system. While it is possible to use a pressurized gas tank with a reducer to provide the working fluid, a complex system is required to automate the operation of the reducer. Alternatively, a support system capable of producing pressurized fluid may be purchased and maintained at increased expense. Further, the piston chamber increases the bulk of the valve assembly. A system utilizing piston operated valves is limited further by its susceptibility to leaks. Fluid leaking about the piston decreases performance of the system. Additionally, in order to move with a live animal, the tubing carrying the working fluid would have to be flexible, further complicating the system and increasing the propensity for leaking. Of course, many animals commonly used in testing have a propensity for gnawing. Considering the fact that a tube's flexibility is normally achieved by utilizing a pliable material, the tube becomes very susceptible to damage from being gnawed upon by the animals. Consequently, use of this type of system may result in exorbitant maintenance costs.
Solenoid operated valves present shortcomings similar to those found with motorized valves. While power lines can be reasonably lightweight, the coil and plunger of the valve must be made of ferrous material, resulting in a heavy and bulky valve. Further, the complexity of the valves means that they are expensive to manufacture and maintain, and may be susceptible to breakdown. A final shortcoming relates to the unfortunate gnawing tendency which was discussed above. Since there may be electricity present in the power line at the time an animal is gnawing on the power line, the consequences of a test animal gnawing through the insulation to the conductor can be quite detrimental to the health of the animal thereby interfering with the collection of data in addition to the added maintenance costs.
Therefore, it is desired to provide a valve which:                is inexpensive to manufacture and maintain;        is lightweight;        can be remotely operated;        is extremely reliable;        contains low dead volume;        is easily adapted for use with many control systems;        is free to move with respect to its activating mechanism;        does not require precise alignment or keying in order to ensure correct operation;        can be easily miniaturized.        